Pieces of Heart can be found in most The Legend of Zelda games. The amount that Link needs to collect in order to get a complete Heart Container is usually four, but in Twilight Princess it is five (to allow the developers to add more sidequests and such in the game without reducing the length of the main quest). Each game has a different amount of Heart Pieces that can be found. Some have only 12, and some have 44 or more. They are not rare, though some of them take a long time to acquire, such as the 50 Gold Skulltula tokens required to get one of the heart pieces in Ocarina of Time.